The purpose of this project is to demonstrate the cellular mechanisms responsible for transport of material along neuronal processes. We have studied axoplasmic transport by observing the movement of intracellular organelles within the neurites of cultured nerve cells. The method, employing high resolution Nomarski microscopy, increases the spatial and temporal resolution 2-3 orders of magnitude above that obtained with biochemical assays of transport. We have employed the divalent cation selective ionophore A23187 to modify the internal milieu of transporting neurons. Microtubules were always found in neurites observed to be transporting organelles, but transport can occur in the absence of microfilaments or neurofilaments. We have discovered that this transport is dependent on the presence of Mg ions, and is blocked by a 100 micron m internal concentration of Ca ions. The determination of the ultrastructural and ionic requirements of organelle motion will hopefully lead to a general molecular explanation of axoplasmic transport. Further definition of the metabolic and ionic requirements of organelle translocation will be sought and the relationship between such translocation and neurite outgrowth studied.